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Abstract:

This image-forming apparatus includes a plurality of photosensitive
drums, a plurality of laser scanning units, and a motor control unit. A
motor control unit detects the time difference between a change point of
the detection signal of a reference color and the change points of colors
targeted for phase correction, and, when the absolute value of the time
difference is greater than a threshold, carries out a rough adjustment
process for reducing the time difference by a drive signal with which a
base period has been changed by a first period change amount and
thereafter carries out a fine adjustment process for reducing the time
difference by a drive signal with which the base period has been changed
by a second period change amount smaller than the first period change
amount.

Claims:

1. An image-forming apparatus, comprising: a plurality of photosensitive
drums provided for every color; a plurality of laser scanning units for
scanning and exposing the corresponding photosensitive drum, each of the
laser scanning units including a laser-light-emitting unit for switching
a laser beam on and off in accordance with image data; a polygon mirror
for reflecting, while rotating, the laser beam emitted by the
laser-light-emitting unit and scanning and expose the corresponding
photosensitive drum, the polygon mirror having a plurality of reflective
surfaces; a polygon motor for rotating the polygon mirror, the rotational
speed of the polygon motor changing in accordance with the frequency of a
provided drive signal; and a light-receiving unit for outputting a
detection signal having an output value which changes when the laser beam
is received, the light-receiving unit being provided within a range of
irradiation with the laser beam by the polygon mirror; and a motor
control unit for: providing the drive signal of a predetermined base
period to the polygon motors and causing the polygon motors to rotate
such that each of the polygon motors rotates at the same speed; detecting
the time difference between a change point of the detection signal of the
laser scanning unit of a reference color and the change points of the
detection signals of the laser scanning units of colors targeted for
phase correction other than the reference color; and, when the absolute
value of the time difference is greater than a predetermined threshold,
carrying out a rough adjustment process in which the drive signal with
which the base period has been shorted or lengthened by a first period
change amount causes the polygon motors of the colors targeted for phase
correction to rotate and the time difference to decrease, or, when the
absolute value is not greater than the threshold, carrying out a fine
adjustment process in which, until the time difference falls within a
predetermined acceptable range, the drive signal with which the base
period has been shortened or lengthened by a second period change amount
smaller than the first period change amount with respect to the base
period causing the polygon motors of the colors targeted for phase
correction to rotate and the time difference to decrease.

2. The image-forming apparatus as set forth in claim 1, comprising one
correction current supply unit for changing, in a similar manner for each
of the laser-light-emitting units, the current flowing to each of the
laser-light-emitting units in accordance with the scanning position in a
main scanning direction, and for changing the light emission level of
each of the laser-light-emitting units and correcting the difference in
energy received by the photosensitive drums in the main scanning
direction.

3. The image-forming apparatus as set forth in claim 1, comprising: a
transfer unit for superimposingly transferring onto paper a toner image
of each color formed on each of the photosensitive drums, and a fixing
unit for fixing, using heat, the toner image transferred onto the paper,
the fixing unit having a built-in heater; the motor control unit, when a
warm-up for increasing the temperature of the fixing unit to the
temperature needed in order to fix the toner image is performed,
detecting the time difference between the change point of the detection
signal of the laser scanning unit of the reference color and the change
points of the detection signals of the laser scanning units of the colors
targeted for phase correction, carrying out the rough adjustment process
when the absolute value of the time difference is greater than the
threshold, and, after the absolute value has reached or fallen below the
threshold due to the rough adjustment process, carrying out instead of
the fine adjustment process an ultrafine adjustment process in which the
drive signal with which the base period has been shortened or lengthened
by a third predetermined period change amount is used to cause the
polygon motors of the colors targeted for phase correction to rotate
until the time difference falls within the acceptable range; the third
period change amount being smaller than the second period change amount
with respect to the base period.

4. The image-forming apparatus as set forth in claim 3, comprising a
temperature sensor for detecting the temperature of the fixing unit; the
motor control unit, when the temperature detected by the temperature
sensor at the start of phase correction is less than a predetermined
first temperature, performing the ultrafine adjustment process instead of
the rough adjustment process until the time difference falls within the
acceptable range.

5. The image-forming apparatus as set forth in claim 4, the motor control
unit, when the temperature detected by the temperature sensor at the
start of phase correction is higher than the predetermined second
temperature, not performing the ultrafine adjustment process but causing
the time difference to fall within the acceptable range using the rough
adjustment process and the fine adjustment process, the second
temperature being a higher temperature than the first temperature.

6. The image-forming apparatus as set forth in claim 3, the first period
change amount, the second period change amount, and the third period
change amount being change amounts for the drive signal within a range
where the rotation of the polygon motors will not be desynchronized.

7. The image-forming apparatus as set forth in claim 3, the warm-up being
performed when a main power source is turned on and when a power-saving
mode returns to a normal mode.

8. The image-forming apparatus as set forth in claim 1, the first period
change amount being the greatest change amount for the drive signal
within a range where the rotation of the polygon motors will not be
desynchronized.

9. The image-forming apparatus as set forth in claim 3, the absolute
value of the second period change amount being not greater than one-half
of the absolute value of the first period change amount, and the absolute
value of the third period change amount being not greater than one-half
of the absolute value of the second period change amount.

10. A method for controlling an image-forming apparatus, the method
comprising: providing a drive signal of a predetermined base period to
polygon motors for reflecting a laser beam and scanning and exposing a
corresponding photosensitive drum, such that each of the polygon motors
rotates at the same speed; causing each of polygon mirrors to rotate by
the polygon motors; causing a light-receiving unit having an output value
that changes when the laser beam is received to output a detection
signal, the light-receiving unit being provided within a range in which
the laser beam is irradiated by the polygon mirrors ; detecting a time
difference between a change point in the detection signal for a reference
color and change points in detection signals for colors targeted for
phase correction other than the reference color; carrying out, when the
absolute value of the time difference is greater than a predetermined
threshold, a rough adjustment process in which the drive signal with
which the base period has been shorted or lengthened by a first period
change amount causes the polygon motors of the colors targeted for phase
correction to rotate and the time difference to be reduced; and carrying
out, when the absolute value is not greater than the threshold, a fine
adjustment process in which, until the time difference falls within a
predetermined acceptable range, the drive signal with which the base
period has been shortened or lengthened by a second period change amount
causes the polygon motors of the colors targeted for phase correction to
rotate and the time difference to decrease, the second period change
amount being smaller than the first period change amount with respect to
the base period.

11. The method for controlling an image-forming apparatus as set forth in
claim 10, laser-light-emitting units being caused to switch a laser beam
on and off in accordance with image data; the laser beams emitted by the
laser-light-emitting units being reflected and the corresponding
photosensitive drum being scanned and exposed; and one correction current
supply unit changing, in a similar manner for each of the
laser-light-emitting units, the current flowing to each of the
laser-light-emitting units in accordance with the scanning position in a
main scanning direction, and changing the light emission level of each of
the laser-light-emitting units; and the difference in the main scanning
direction in regard to energy received by the photosensitive drums being
corrected.

12. The method for controlling an image-forming apparatus as set forth in
claim 10, a toner image of each color formed on each of the
photosensitive drums being superimposingly transferred onto paper; a
fixing unit being made to fix the transferred toner images to the paper
using heat; the time difference between a change point in the detection
signal of the laser-scanning unit for a reference color and change points
in detection signals of the laser-scanning unit for colors targeted for
phase correction being detected when warm-up is performed for increasing
the temperature of the fixing unit to a temperature needed to fix the
toner images; the rough adjustment process being carried out when the
absolute value of the time difference is greater than the threshold; and
an ultrafine adjustment process being carried out instead of the fine
adjustment process, in which, after the absolute value has reached or
fallen below the threshold due to the rough adjustment process, the drive
signal with which the base period has been shortened or lengthened by a
third predetermined period change amount is used to cause the polygon
motors of the colors targeted for phase correction to rotate until the
time difference falls within the acceptable range, the third period
change amount being smaller than the second period change amount with
respect to the base period.

13. The method for controlling an image-forming apparatus as set forth in
claim 12, a temperature sensor being made to detect the temperature of
the fixing unit when the phase correction is to start, and when the
temperature detected by the temperature sensor is less than a
predetermined first temperature, only the ultrafine adjustment process
and not the rough adjustment process being carried out until the time
difference falls within the acceptable range.

14. The method for controlling an image-forming apparatus as set forth in
claim 13, a temperature sensor being made to detect the temperature of
the fixing unit when the phase correction is to start, and when the
temperature detected by the temperature sensor is higher than a
predetermined second temperature, the time difference being made fall
within the acceptable range by the rough adjustment process and the fine
adjustment process, without the ultrafine adjustment process being
carried out; and the second temperature being a higher temperature than
the first temperature.

15. The method for controlling an image-forming apparatus as set forth in
claim 12, the first period change amount, the second period change
amount, and the third period change amount being change amounts for the
drive signal within a range where the rotation of the polygon motors will
not be desynchronized.

16. The method for controlling an image-forming apparatus as set forth in
claim 12, the warm-up being performed when a main power source is turned
on and when a power-saving mode returns to a normal mode.

17. The method for controlling an image-forming apparatus as set forth in
claim 10, the first period change amount being the greatest change amount
for the drive signal within a range where the rotation of the polygon
motors will not be desynchronized.

18. The method for controlling an image-forming apparatus as set forth in
claim 12, the absolute value of the second period change amount being not
greater than one-half of the absolute value of the first period change
amount, and the absolute value of the third period change amount being
not greater than one-half of the absolute value of the second period
change amount.

Description:

[0001] This application is based upon and claims the benefit of priority
from the corresponding Japanese Patent Application No. 2011-230695 filed
Oct. 20, 2011, the entire contents of which are incorporated herein by
reference.

BACKGROUND

[0002] The present disclosure relates to an image-forming apparatus for
scanning to expose a photosensitive drum to a laser to form an image
(toner image).

[0003] Conventionally, a rotating polygon mirror may be made to reflect a
laser beam and a lens, mirror, or the like may be used to form an
electrostatic latent image on a photosensitive drum, thus forming a toner
image. When such a laser beam is reflected and scanned to expose the
photosensitive drum, it is necessary to appropriately control a variety
of parameters, such as the start timing for the scanning and exposure of
each of the lines and the rotational speed of the polygon mirror.

[0004] One known example is an image-forming apparatus for causing a
rotating polygonal mirror to reflect an exposure beam controlled in
accordance with an image clock and using a rotating process member to
form/develop/transfer an electrostatic latent image and obtain an image,
wherein the speed variance of the process member is detected and the
rotational speed of the rotational polygonal mirror, the frequency of the
image clock, and the light intensity of the exposure beam are controlled
in accordance with the detected speed variance.

[0005] Some image-forming apparatuses form a toner image in each color on
a plurality of photosensitive drums and superimpose the toner images in
each color to carry out color printing (also sometimes called a tandem
scheme). Because of the superimposition of the toner images in each
color, the toner images in each color sometimes have uneven densities
and/or misaligned positions, whereupon the image quality is degraded. In
view whereof, the phases of the polygon mirrors (polygon motors) for each
color are sometimes matched.

[0006] For example, the inputting of a print start command into an
operation panel, the receipt of image data, or the like serves as a
trigger for printing to start. In association with the start of printing,
the polygon motors for each color, which rotate the polygon mirrors, are
rotated up to a reference speed that has been determined in advance.
Then, in order to be able to match the angle of rotation (phase) of the
polygon mirror (polygon motor) for a color serving as a reference, the
rotational speed of the polygon motors for the colors other than the
reference color (colors targeted for phase correction) are intentionally
shifted from the reference speed. The phase difference is continually
reduced and, once the phase difference reaches an acceptable range, the
polygon motors for the colors targeted for phase correction are returned
to the reference speed.

[0007] From the standpoint of the ability of the polygon motors to track
and respond to speed variance, it is desirable to lower as much as
possible the amount of change from the reference speed to change the
rotational speeds of the polygon motors of the colors targeted for phase
correction, in order to be able to accurately and precisely match the
phases of each of the polygon mirrors. For this reason, during the
correction of the phase difference, it is more preferable for the
rotational speed of the polygon motors not to be over-shifted with
respect to the reference speed.

[0008] On the other hand, from the standpoint of starting printing as
quickly as possible, it is desirable to rapidly complete the correction
of the phase differences of each of the polygon motors and to shorten the
time needed to bring an exposure device to a state where printing is
possible. However, when the amount of change from the reference speed is
lowered as much as possible and the rotational speed of the polygon
motors for the colors targeted for phase correction is changed to correct
the phase difference, a problem emerges in that it is a long time until
the phase difference between the polygon mirror (polygon motor) of the
reference color and the polygon mirrors (polygon motors) of the colors
targeted for phase correction falls within the acceptable range.

[0009] With the above-mentioned known image-forming apparatus, a variety
of processes and controls such as for changing the image clock and
changing the intensity of the exposure beam are performed to prevent a
degradation in the quality of the image. However, there is no adjustment
for the phase difference between the polygon mirrors (polygon motors) for
each color. As such, when the amount of change from the reference speed
is lowered as much as possible and the rotational speed of the polygon
motors for the colors targeted for phase correction is changed to correct
the phase difference, it is not possible to address the problem which
emerges in that it is a long time until the phase difference falls within
the acceptable range.

SUMMARY

[0010] With the foregoing problems in view, it is an objective to curtail
the time required for phase correction while the phase difference between
the polygon mirror of the reference color and the polygon mirrors of the
colors targeted for phase correction is accurately being made fall within
the acceptable range.

[0011] In order to overcome the problems, an image-forming apparatus
according to a first aspect of the present disclosure comprises a
plurality of photosensitive drums, a plurality of laser scanning units,
and a motor control unit. The plurality of photosensitive drums are
provided for every color. Each of the plurality of laser scanning units
comprises a laser-light-emitting unit for switching a laser beam on and
off in accordance with image data, a polygon mirror for reflecting the
laser beam emitted by the laser-light-emitting unit while also rotating
to scan and expose the corresponding photosensitive drum, the polygon
mirror having a plurality of reflective surfaces, a polygon motor for
rotating the polygon mirror, the rotational speed of the polygon motor
changing in accordance with the frequency of a provided drive signal, and
a light-receiving unit for outputting a detection signal having an output
value which changes when the laser beam is received, the light-receiving
unit being provided within a range of irradiation with the laser beam by
the polygon mirror. The laser scanning units scan and expose the
corresponding photosensitive drum and form a toner image of respectively
different colors. The motor control unit provides the drive signal of a
predetermined base period to the polygon motors and causes the polygon
motors to rotate such that each of the polygon motors rotates at the same
speed, detects the time difference between a change point of the
detection signal of the laser scanning unit of a reference color and the
change points of the detection signals of the laser scanning units of
colors targeted for phase correction other than the reference color is
detected, and, when the absolute value of the time difference is greater
than a predetermined threshold, carries out a rough adjustment process in
which the drive signal with which the base period has been shorted or
lengthened by a first period change amount causes the polygon motors of
the colors targeted for phase correction to rotate and the time
difference to decrease, or, when the absolute value is not greater than
the threshold, carries out a fine adjustment process in which, until the
time difference falls within a predetermined acceptable range, the drive
signal with which the base period has been shortened or lengthened by a
second period change amount smaller than the first period change amount
with respect to the base period causes the polygon motors of the colors
targeted for phase correction to rotate and the time difference to
decrease.

[0012] Further features and advantages of the present disclosure will
become apparent from the description of embodiments given below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic front cross-sectional view illustrating one
example of a multifunctional peripheral.

[0014]FIG. 2 is an enlarged, schematic cross-sectional view of an image
formation unit.

[0015]FIG. 3 is a schematic view illustrating one example of an exposure
device.

[0016]FIG. 4 is a block diagram illustrating one example of a hardware
configuration for a multifunctional peripheral.

[0017]FIG. 5 is a block diagram illustrating one example of a hardware
configuration relating to the switching on and off of a
laser-light-emitting unit.

[0018]FIG. 6 is a graph illustrating one example of the energy received
by a photosensitive drum (the received light intensity) at each of the
positions in a main scanning direction.

[0019]FIG. 7 is a graph illustrating one example of the output ratio of
the laser-light-emitting unit when a correction is performed for the
light-emitting level in accordance with the position of the
photosensitive drum in the main scanning direction.

[0020]FIG. 8 is a block diagram illustrating one example of a hardware
configuration relating to the rotation of each of the polygon mirrors.

[0021]FIG. 9 is a block diagram illustrating one example of a power
supply system.

[0023] FIG. 11 is a flow chart for illustrating one example of a flow for
a phase correction control of each of the polygon mirrors during a normal
mode.

[0024]FIG. 12 is a timing chart for illustrating one example of a
detection signal outputted by the light-receiving unit before the start
of phase correction.

[0025]FIG. 13 is a timing chart for illustrating one example of a
detection signal outputted by the light-receiving unit during phase
correction control.

[0026]FIG. 14 is a timing chart for illustrating one example of a
detection signal outputted by the light-receiving unit after the
completion of phase correction.

[0027]FIG. 15 is a flow chart illustrating one example of a flow for a
phase correction control of each of the polygon mirrors when a main power
source is turned on or at the time of return to the normal mode.

[0028]FIG. 16 is a flow chart illustrating one example of a flow for a
phase correction control of each of the polygon mirrors when a main power
source is turned on or at the time of return to the normal mode.

DETAILED DESCRIPTION

[0029] Provided below is a description of an embodiment of the present
disclosure, with reference to FIGS. 1 to 16. This description relates to
an example in which a multifunctional peripheral 100 serves as the
image-forming apparatus. However, the configurations, arrangements, and
other various elements described in this embodiment do not limit the
scope of the disclosure but rather are provided merely by way of
descriptive example.

[0030] (Summary of the Image-Forming Apparatus)

[0031] The description shall first relate to a summary of the
multifunctional peripheral 100 according to an embodiment, with reference
to FIGS. 1 and 2. FIG. 1 is a schematic front cross-sectional view
illustrating one example of the multifunctional peripheral 100. FIG. 2 is
an enlarged, schematic cross-sectional view of an image formation unit
21.

[0032] As illustrated in FIG. 1, the multifunctional peripheral 100 of the
embodiment has a document cover 1a on an uppermost part. An operation
panel 1b is also provided to the top of a front surface of the
multifunctional peripheral 100. An image reading unit 1c, paper feed unit
1d, conveyor unit 1 e, image formation part 2 (including an exposure
device 4), intermediate transfer unit 3a, fixing unit 3b, and the like
are provided to the main body of the multifunctional peripheral 100.

[0033] As illustrated by the dashed line in FIG. 1, the operation panel 1b
is provided to the top of the front surface of the multifunctional
peripheral 100. The operation panel 1b is also provided with a display
unit 11. A touch panel unit 12 is provided to an upper surface of the
display unit 11. Also, for example, the operation panel 1b is provided
with a keypad unit 13 and a start key 14.

[0034] The document cover 1a has a pivot point behind the plane of the
drawing in FIG. 1. The document cover 1a is able to open and close in the
vertical direction of the paper plane. During reading of a document, the
document cover 1a presses a document that has been placed on a contact
glass 15 used for placing and reading documents.

[0035] The image reading unit 1c reads the document and forms image data
relating to the document. The image reading unit 1c reads the document
placed on the contact glass 15 for placement/reading, and generates the
image data.

[0036] For example, the paper feed unit 1d includes a cassette 16. A paper
feed roller 17 issues paper to the conveyor unit 1e. The conveyor unit 1e
guides the paper supplied from the paper feed unit 1d, to a discharge
tray 18 by way of the intermediate transfer unit 3a and the fixing unit
3b. A pair of conveyor rollers 19a and/or a pair of resist rollers 19b
and the like are provided to the conveyor unit 1e.

[0037] As illustrated in FIGS. 1 and 2, the image formation part 2
includes image formation units 21 and an exposure device 4 for four
different colors. More specifically, with respect to the image formation
unit 21, the multifunctional peripheral 100 is provided with an image
formation unit 21Bk for forming a black image, an image formation unit
21Y for forming a yellow image, an image formation unit 21M for forming a
magenta image, and an image formation unit 21C for forming a cyan image.

[0038]FIG. 2 shall now be used to provide a more detailed description of
each of the image formation units 21Bk-21C. Respective photosensitive
drums 22Bk-22C (four different colors, where 22Bk is for black, 22C is
for cyan, 22M is for magenta, and 22Y is for yellow) provided to each of
the image formation units 21Bk-21C carry a toner image on a peripheral
surface. Respective electrification devices 23 electrify the
photosensitive drums 22 with a constant potential. The exposure device 4
switches a laser beam (depicted by a dashed line) on and off to produce
output, on the basis of a signal indicative of the switching on or off of
the beam as generated on the basis of image data. The exposure device 4
scans to expose each of the photosensitive drums 22Bk-22C after
electrification, and form an electrostatic latent image. Respective
development devices 24 accommodate a developing agent for the
corresponding color. Respective cleaning devices 25 clean the
photosensitive drums 22.

[0040] The intermediate transfer belt 32 is strapped onto the drive roller
33 and the like. The drive roller 33 is connected to a motor or similar
drive mechanism (not shown). The intermediate transfer belt 32 is turned
by the rotational drive of the drive roller 33. The drive roller 33 and
the second transfer roller 35 sandwich the intermediate transfer belt 32.
The toner images (for each color, i.e., for black, yellow, cyan, and
magenta) formed by each of the image formation units 21Bk-21C are
sequentially superimposed and undergo primary transfer to the
intermediate transfer belt 32. Thereafter, the toner images are
transferred to the paper by the secondary transfer roller 35 to which the
predetermined voltage has been applied.

[0041] The fixing unit 3b applies heat and pressure to fix the toner
images having undergone secondary transfer to the paper. The paper onto
which the toner images have been transferred is passed through the nip
portion of a heating roller 37 and a pressure roller 38, whereby heat and
pressure are applied. As a result, the toner images are fixed to the
paper, and the paper is discharged to the discharge tray 18.

[0042] (Configuration of the Exposure Device 4)

[0043] The description shall now relate to one example of the exposure
device 4 according to the embodiment, with reference to FIG. 3. FIG. 3 is
a schematic view illustrating one example of the exposure device 4. In
FIG. 3, the depiction is of the configuration for one color.

[0045] The exposure device 4 of the present embodiment includes the laser
scanning unit 40Bk for black, the laser scanning unit 40Y for yellow, the
laser scanning unit 40M for magenta, and the laser scanning unit 40C for
cyan, for a total of four laser scanning units 40 (for the sake of
simplicity, only one is depicted in FIG. 3).

[0046] Laser-light-emitting units 5Bk-5C emit a laser beam. The exposure
device 4 of the present embodiment includes the laser-light-emitting unit
5Bk for black, the laser-light-emitting unit 5Y for yellow, the
laser-light-emitting unit 5M for magenta, and the laser-light-emitting
unit 5C for cyan.

[0047] The polygon mirror 6 for reflecting the laser beam is also provided
so as to correspond to each of the laser-light-emitting units 5Bk-5C. The
lens 41 is provided respectively between each of the laser-light-emitting
units 5Bk-5C and polygon mirrors 6Bk-6C (for the sake of simplicity, the
reference numerals for the lenses 41 omit an indication of the
distinction between the colors Bk, Y, M, and C).

[0048] The polygon motor 7 is provided to each of the polygon mirrors
6Bk-6C. In the present embodiment, the exposure device 4 includes the
polygon motor 7Bk for black, the polygon motor 7Y for yellow, the polygon
motor 7M for magenta, and the polygon motor 7C for cyan, for a total of
four polygon motors 7.

[0049] The exposure device 4 is also provided with the f-theta lens 42 for
evening, in a main scanning direction, the scanning and exposure speed of
the photosensitive drum 22 by the laser beams emitted by each of the
polygon mirrors 6Bk-6C, as well as with the mirror 43 for reflecting the
laser beams toward each of the photosensitive drums 22Bk-22C (for the
sake of simplicity, the reference numerals for the f-theta lenses 42 and
the mirrors 43 omit an indication of the distinction between the colors
Bk, Y, M, C).

[0050] Each of the laser scanning units 40 (40Bk-40C) irradiates each of
the photosensitive drums 22Bk-22C from the exposure device 4 with a laser
beam, and an electrostatic latent image matched to the image data is
formed on each of the photosensitive drums 22Bk-22C.

[0051] Each of the laser scanning units 40 (40Bk-40C) includes the
light-receiving unit 8, which has been provided in an irradiation range
for irradiation of the laser beam in the main scanning direction (within
a scanning range), and outside of an irradiation range for irradiating
the photosensitive drums 22. The exposure device 4 of the present
embodiment includes a light-receiving unit 8Bk for black, a
light-receiving unit 8Y for yellow, a light-receiving unit 8M for
magenta, and a light-receiving unit 8C for cyan, for a total of four
light-receiving units 8. The output current (output voltage) for each of
the light-receiving units 8Bk-8C changes between the presence and absence
of laser beam irradiation. For example, each of the light-receiving units
8Bk-8C is a circuit including a light-receiving element (for example, a
photodiode) and the like. The timing for exposing (writing on) the
photosensitive drums 22 at respective lines is taken on the basis of the
outputs of each of the light-receiving units 8Bk-8C.

[0052] (Hardware Configuration of the Multifunctional Peripheral 100)

[0053] The description shall now relate to the hardware configuration of
the multifunctional peripheral 100 according to the embodiment, on the
basis of FIG. 4. FIG. 4 is a block diagram for illustrating one example
of the hardware configuration for the multifunctional peripheral 100.

[0054] As illustrated in FIG. 4, the multifunctional peripheral 100 of the
present embodiment has a main control unit 9 on the interior. The main
control unit 9 controls each of the parts of the multifunctional
peripheral 100. For example, the main control unit 9 includes a CPU 91, a
storage unit 92, an image processing unit 93, and the like.

[0055] The CPU 91 is a central computation and processing device, and
performs computations and controls each of the parts of the
multifunctional peripheral 100 on the basis of a control program stored
and deployed in the storage unit 92. The storage unit 92 is constituted
of a combination of volatile and non-volatile storage devices, such as
ROM, RAM, and flash ROM. For example, the storage unit 92 stores, inter
alia, the control program and control data for the multifunctional
peripheral 100.

[0056] The main control unit 9 is connected so as to be able to
communicate with an engine control unit 90 for controlling a portion
relating to printing (a printing engine unit 10). The engine control unit
90 turns on and off the exposure device 4, image formation, motors for
rotating the various rotating bodies, and the like, on the basis of a
command from the main control unit 9, and controls the portions and
members that relate to printing. The engine control unit 90 maintains
actual control over the behaviors of the paper feed unit 1d, the conveyor
unit 1e, the image formation part 2, the exposure device 4, the
intermediate transfer unit 3a, the fixing unit 3b, and the like.

[0057] The main control unit 9 also includes a communication unit 94. The
communication unit 94 includes, inter alia, a chip, memory, connector,
and circuit for communication. The communication unit 94 and a computer
200 (for example, a personal computer 200, a server, or the like) are
connected together so as to be able communicate via a network or cable.
Printing data which includes data indicative of what is to be printed and
data for printing settings is inputted via the communication unit 94 from
the computer 200 into the main control unit 9. Also inputted into the
main control unit 9 is image data relating to the document that has been
read by the image reading unit 1c. The image processing unit 93 subjects
the image data from the computer 200 or from the image reading unit 1c to
a variety of image processes, such as enlarging, shrinking, contrast
stretching, and data format conversion, in accordance with the settings
on the operation panel 1b and/or the settings in the printing data. The
image processing unit 93 then sends the image-processed image data to the
exposure device 4. On receiving the image data, the exposure device 4
scans and exposed each of the photosensitive drums 22Bk-22C.

[0058] The main control unit 9 is also connected, inter alia, to the
operation panel 1b and the image reading unit 1c. The main control unit 9
controls the behavior of each of the parts on the basis of the settings
made with the operation panel 1b such that image formation is carried out
properly on the basis of the image data obtained from the reading of the
document by the image reading unit 1c and the control program and data in
the storage unit 92.

[0059] (Switching On and Off of the Laser-Light-Emitting Units 5)

[0060] The description shall now relate to a summary of the on/off
switching control of each of the laser-light-emitting units 5Bk-5C
according to the embodiment, with reference to FIGS. 5 to 7. FIG. 5 is a
block diagram illustrating one example of a hardware configuration
relating to the switching on and off of the laser-light-emitting units 5.
FIG. 6 is a graph illustrating one example of the energy received by the
photosensitive drums 22 (the received light intensity) at each of the
positions in the main scanning direction. FIG. 7 is a graph illustrating
one example of the output ratio of the laser-light-emitting units 5 when
a correction is performed for the light-emitting level in accordance with
the position of the photosensitive drums 22 in the main scanning
direction.

[0061] As illustrated in FIG. 5, in the multifunctional peripheral 100 of
the present embodiment, the engine control unit 90 controls the switching
on and off of each of the laser-light-emitting units 5Bk-5C. The engine
control unit 90 controls the switching on and off of each of the
laser-light-emitting units 5Bk-5C on the basis of the image data.
Separately from the engine control unit 90, there may also be provided a
dedicated IC or similar circuit for controlling the switching on and off
of the laser-light-emitting units 5Bk-5C on the basis of a command from
the engine control unit 90.

[0062] The exposure device 4 is also provided with one correction current
supply unit 51 and a plurality of reference current supply units 52 for
supplying a current to each of the laser-light-emitting units 5Bk-5C.
More specifically, a reference current supply unit 52Bk for black, a
reference current supply unit 52Y for yellow, a reference current supply
unit 52M for magenta, and a reference current supply unit 52C for cyan
are provided.

[0063] One reference current supply unit 52 is respectively provided to
each of the laser-light-emitting units 5Bk-5C (for a total of four
reference current supply units). Each of the reference current supply
units 52 outputs and supplies to each of the laser-light-emitting units
5Bk-5C a current that has been adjusted such that each of the
laser-light-emitting units 5Bk-5C emits light on the same level (a
current that has been adjusted such that the light emission level of each
of the laser-light-emitting units 5Bk-5C reaches a reference level), in
accordance with the light emission properties of each of the
laser-light-emitting units 5Bk-5C. A reference output value for the
currents respectively determined for each of the laser-light-emitting
units 5Bk-5C is stored in a memory 901 (for example, a flash ROM). When
the photosensitive drums 22 are to be exposed, a value indicative of the
magnitude of current that is to be outputted for each of the reference
current supply units 52 (the reference output value) is acquired from the
memory 901, and the reference output value is sent to each of the
reference current supply units 52.

[0064] When each of the photosensitive drums 22Bk-22C is to be exposed for
printing, the engine control unit 90 respectively sends the reference
output value to each of the reference current supply units 52. The
reference current supply units 52 output a current in accordance with the
commanded reference output value from the engine control unit 90.
Thereby, each of the laser-light-emitting units 5Bk-5C reach
substantially the same light emission level (reference output or
reference emitted light intensity), provided that they are at the same
scanning position. In the present embodiment, the engine control unit 90
sends the reference output value to each of the reference current supply
units 52 by a digital value. For this reason, each of the reference
current supply units 52 is, for example, a digital/analog converter (DAC)
for outputting a current in accordance with the magnitude of the
reference output value.

[0065] By contrast, one correction current supply unit 51 is provided to
the laser-light-emitting units 5Bk-5C. The correction current supply unit
51 outputs a current for correcting the light emission level of a beam
irradiated in accordance with the positions of the photosensitive drums
22 in the main scanning direction (in accordance with each pixel), and
supplies the same current (depicted as "i1" in FIG. 5) to each of the
laser-light-emitting units 5Bk-5C.

[0066] When the photosensitive drums 22 are to be exposed, the engine
control unit 90 sends a value indicative of the magnitude of current that
is to be outputted (a correction output value) to the correction current
supply unit 51. The correction current supply unit 51 outputs a current
in accordance with the commanded correction output value from the engine
control unit 90. In the present embodiment, the engine control unit 90
sends the correction output value to the correction current supply unit
51 by a digital value. For this reason, the correction current supply
unit 51 is, for example, a digital/analog converter (DAC) for outputting
a current in accordance with the magnitude of the correction output
value. The correction current supply unit 51 and the reference current
supply units 52 may be of the same circuit (of the same type of circuit).

[0067] The description thus now relates to the variance in the energy
received by the photosensitive drums 22 (received light intensity) at
each of the positions in the main scanning direction, with reference to
FIG. 6. It is specifically assumed that the energy received by the
photosensitive drum 22 at the pixel portion undergoing exposure (the
light intensity of the received laser beam) is desirably uniform in the
main scanning direction (the horizontal line in FIG. 6) because of the
potential to cause color unevenness or the like.

[0068] However, as described above, the polygon mirrors 6, the f-theta
lenses 42, and the mirrors 43, inter alia, are provided in the exposure
device 4 in order for the laser beams to reach the photosensitive drums
22 from each of the laser-light-emitting units 5Bk-5C. In the exposure
device 4 of the present embodiment, each of the polygon mirrors 6Bk-6C
are provided so as to correspond to a center position of the
photosensitive drums 22 in the main scanning direction. For this reason,
greater separation from the center position of the photosensitive drums
22 in the main scanning direction correlates to a greater angle of
incline at which the laser beams are incident on the f-theta lenses 42,
the mirrors 43, and the photosensitive drums 22. The reflectivity of the
mirrors 43 changes depending on the angle of incidence of the laser
beams, and the transmittance (attenuation rate) of the f-theta lenses 42
changes depending on the angle of incidence of the laser beams. In
general, a more acute angle of incidence correlates to a greater degree
to which the beams after transmission are attenuated.

[0069] For this reason, even though the light emitted by the laser beams
is at a constant level for the scanning of the photosensitive drums 22,
the energy received by the photosensitive drums 22 varies in accordance
with the position in the main scanning direction, as indicated in FIG. 6
by the upwardly curved line. More specifically, in the multifunctional
peripheral 100 of the present embodiment, the energy received by the
photosensitive drums 22 is increasingly attenuated closer to the end part
of the photosensitive drums 22.

[0070] Thus, as illustrated in FIG. 7, the engine control unit 90 of the
present embodiment performs a similar correction for each of the
laser-light-emitting units 5Bk-5C, in which the current being supplied is
increased more closer to the end part of the photosensitive drums 22.
This causes the energy received by the photosensitive drums 22 to be
uniform in the main scanning direction, as illustrated by the horizontal
line in FIG. 6. In order to correct the light emission levels of each of
the laser-light-emitting units 5Bk-5C in accordance with the exposure
position in the main scanning direction, the engine control unit 90
causes the correction current supply unit 51 to change (adjust) the
current being outputted (supplied) to each of the laser-light-emitting
units 5Bk-5C during scanning (exposure) of a single line.

[0071] Correction data indicative of which correction output value is to
be given (data indicative of the correction output value for each pixel)
in accordance with the position of the photosensitive drums 22 in the
main scanning direction (in accordance with the pixel) is stored in the
memory 901, which is connected to the engine control unit 90. The memory
901 may also be built into the engine control unit 90. When the
photosensitive drums 22 are to be exposed, the engine control unit 90
acquires the correction data from the memory 901 and sequentially sends
the correction output value to the correction current supply unit 51 on
the basis of the correction data.

[0072] As illustrated in FIG. 5, a current in which the current i1
outputted by the correction current supply unit 51 has been superimposed
onto the current outputted by the corresponding reference current supply
unit 52 is sent to each of the laser-light-emitting units 5Bk-5C. When
scanning is to be performed to expose the photosensitive drums 22, each
of the laser-light-emitting units 5Bk-5C receives this current and
outputs a laser beam.

[0073] (Rotational Control of each of the Polygon Mirrors 6Bk-6C)

[0074] The description shall now relate to a summary of the rotational
control of each of the polygon mirrors 6Bk-6C (each of the polygon motors
7Bk-7C) according to the embodiment, with reference to FIG. 8. FIG. 8 is
a block diagram illustrating one example of a hardware configuration
relating to the rotation of each of the polygon mirrors 6Bk-6C.

[0075] As illustrated in FIG. 8, in the multifunctional peripheral 100 of
the present embodiment, the engine control unit 90 controls the on/off
status and rotational speed of each of the polygon motors 7Bk-7C. The
engine control unit 90 causes each of the polygon motors 7Bk-7C to rotate
when printing starts as well as during printing. Separately from the
engine control unit 90, there may also be provided a dedicated IC or
similar circuit for controlling the rotation of each of the polygon
motors 7Bk-7C on the basis of a command from the engine control unit 90.

[0076] Each of the polygon motors 7Bk-7C is a similar motor (a motor of a
similar specification), which receives the input of a drive signal (for
example, a clock signal) and rotates. The rotational speed of each of the
polygon motors 7Bk-7C changes in accordance with the period (frequency)
of the drive signal. The engine control unit 90 sends a command to a
drive signal generation unit 902 and, at the time of printing, causes a
drive signal of the same period (frequency) to be inputted to each of the
polygon motors 7Bk-7C. This makes it possible for each of the polygon
motors 7Bk-7C to rotate at the same speed (synchronously) during
printing.

[0077] A synchronization signal indicative of the fact that rotation is
being performed in accordance with the period (frequency) of the drive
signal is outputted from each of the polygon motors 7Bk-7C to the drive
signal generation unit 902 (may be the engine control unit 90). This
makes it possible for the engine control unit 90 to communicate with the
drive signal generation unit 902 and check whether or not the synchronous
rotation each of the polygon motors 7Bk-7C has shifted.

[0078] The drive signal generation unit 902 is also able to alter the
period (frequency) of the drive signal. For example, the drive signal
generation unit 902 is a pulse-width modulation (PWM) circuit capable of
altering the period (frequency) of the drive signal in accordance with a
command from the engine control unit 90.

[0079] In this manner, the engine control unit 90 controls the on/off
status of each of the polygon motors 7Bk-7C. More specifically, in order
to cause each of the polygon motors 7Bk-7C to rotate, the engine control
unit 90 sends to the drive signal generation unit 902 a generation
command for the drive signal as well as data indicative of the period
(frequency) of the drive signal that is to be generated, and controls the
on/off status and rotational speed of each of the polygon motors 7Bk-7C.
When scanning is to be performed to expose each of the photosensitive
drums 22Bk-22C, the engine control unit 90 causes each of the polygon
motors 7Bk-7C to rotate and, when a print job has been completed, causes
each of the polygon motors 7Bk-7C to stop.

[0080] The output of each of the light-receiving units 8Bk-8C is also
inputted to the engine control unit 90. The engine control unit 90 is
able to check, inter alia, whether the rotational speeds of each of the
polygon motors 7Bk-7C are identical by checking the period of the change
in output of each of the light-receiving units 8Bk-8C. For example, the
light-receiving unit 8 for black serves as a reference for the engine
control unit 90 to determine the timing for writing on the lines of each
of the laser-light-emitting units 5Bk-5C. The use of the change in output
of each of the light-receiving units 8Bk-8C as a synchronization signal
makes it possible to match the write position for each of the lines.

[0081] (Normal Mode and Power Saving Mode)

[0082] The description shall now relate to a normal mode and power saving
mode in the multifunctional peripheral 100 of the embodiment, with
reference to FIGS. 9 and 10. FIG. 9 is a block diagram illustrating one
example of a power supply system. FIG. 10 is a block diagram for
illustrating an operation input detection unit.

[0083] Firstly, as illustrated in FIG. 9, the multifunctional peripheral
100 is provided with a power source unit 95 for generating a variety of
different voltages and for supplying power at an appropriate voltage to
each of the portions constituting the multifunctional peripheral 100. The
power source unit 95 is provided with power source device 96 for
generating a plurality of voltage types required for the behaviors of the
multifunctional peripheral 100, the power source device comprising, inter
alia, a rectifier circuit, a booster circuit, and a step-down circuit,
and being connected to a commercially available power source.

[0084] A main switch 97 is provided in order to switch on and off the
connection between the power source device 96 and the commercially
available power source. For example, the main switch 97 is a rocker
switch, and is provided to a side surface or the like of the
multifunctional peripheral 100. A user is able to switch the on/off
status of the main power source of the multifunctional peripheral 100
using the main switch 97.

[0085] As illustrated in FIG. 9, the power source unit 95 also includes a
switch unit 98. The switch unit includes a plurality of semiconductor
switches or similar switches. The switch unit 98 turns on and off the
power supply to each of the parts of the multifunctional peripheral 100,
such as to the main control unit 9. With the on/off switch, the switch
unit 98 switches between distributing and blocking power to the main
control unit 9, the image reading unit 1c, the operation panel 1b, the
printing engine unit 10, and the like. In other words, the power source
unit 95 uses the switch unit 98 to open or close a power supply line from
the power source device 96 to the main control unit 9 and elsewhere, and
controls the on/off state of the power supply to each of the parts.

[0086] In the normal mode, the power source unit 95 supplies power to all
portions within the multifunctional peripheral 100, including the main
control unit 9, the image reading unit 1c, the operation panel 1b, and
the printing engine unit 10. The power source unit 95 maintains the
multifunctional peripheral 100 in a state where all types of jobs can be
executed. When the main power source is turned on by the main switch 97,
the power source unit 95 supplies power within the normal mode.

[0087] By contrast, when a condition for transitioning to the power saving
mode is fulfilled, the main control unit 9 transitions the mode of the
multifunctional peripheral 100 to the power saving mode. In association
with the transition to the power saving mode, the power source unit 95
stops the power supply to the main control unit 9, the image reading unit
1c, the operation panel 1b, the printing engine unit 10, and elsewhere,
and reduces the power consumption.

[0088] An example of a condition for transitioning to the power saving
mode could be when a predetermined transition period has elapsed since
the normal mode came into effect without there being any operation or
input with respect to an operation input detection unit (to be described
in greater detail below) or, alternatively, without there being any
operation or input with respect to the operation input detection unit
since the complete execution of a job. In other words, the condition for
transitioning to the power saving mode could be when the predetermined
transition period (for example, several minutes to several tens of
minutes, can be set using the operation panel 1b) has elapsed with a
standby state remaining in effect.

[0089] There are a plurality of the operation input detection units
provided within the multifunctional peripheral 100. During the normal
mode, the output of each of the operation input detection units is
transmitted to the main control unit 9. The main control unit 9
recognizes whether or not the predetermined transition period has elapsed
without there being any operation or input with respect to the operation
input detection units on the basis of the output of each of the operation
input detection units.

[0090] Firstly, an example of an operation input detection unit within the
main control unit 9 is the communication unit 94. When the communication
unit 94 has received image data for printing or print settings data from
the external computer 200, the main control unit 9 recognizes that an
operation or input has been made with respect to the multifunctional
peripheral 100. As another example, the touch panel unit 12 of the
operation panel 1b is used as an operation input detection unit. When the
touch panel unit 12 is pressed, the main control unit 9 recognizes that
an operation or input has been made with respect to the multifunctional
peripheral 100.

[0091] An insertion/removal detection sensor 16s for detecting insertion
or removal of the cassette 16 or a cover open/close detection sensor 1fs
for detecting the opening or closing of the cover can also be used as
operation input detection units. The main control unit 9 recognizes an
operation or input to the multifunctional peripheral 100 on the basis of
the output of the insertion/removal detection sensor 16s or the cover
open/close detection sensor 1fs. As another example, an open/close
detection sensor 1cs for detecting raising or lowering (opening/closing)
of the document cover 1a of the image reading unit 1c can also be used as
an operation input detection unit. The main control unit 9 recognizes an
operation or input to the multifunctional peripheral 100 on the basis of
the output of the open/close detection sensor 1cs. The open/close
detection sensor 1cs detects whether the document cover 1a is open or
closed. For example, the open/close detection sensor 1cs is provided to a
position in contact with the document cover 1a on an upper surface of the
image reading unit 1c. The open/close detection sensor 1cs may be an
interlocking-type switch in contact with a lower surface of the document
cover 1a, or may be a reflective optical sensor, provided that it is able
to detect an open or closed state.

[0092] When the normal mode is in effect, the main control unit 9 resets
the count for the transition period upon recognition of an operation or
input to the multifunctional peripheral 100 by an operation input
detection unit. However, when the transition period elapses without there
being any operation or input with respect to each of the operation input
detection units, the main control unit 9 commands the power source unit
95 to transition to the power saving mode. The power supply mode of the
power source unit 95 is thereby made to be the power saving mode.

[0093] In the power saving mode, the power source unit 95 stops the supply
of power to the main control unit 9, the image reading unit 1c, the
operation panel 1b, the print engine unit 10, and the like. For this
reason, the state in effect is such that copying, scanning, sending, and
other functions of the multifunctional peripheral 100 cannot be used. As
such, in order for a user to be able to use the multifunctional
peripheral 100, it is necessary for the power supply mode of the power
source unit 95 to be returned from the power saving mode to the normal
mode and for the supply of power to the main control unit 9, the image
reading unit 1c, the operation panel 1b, the print engine unit 10, the
document cover 1a, and the like to be restored.

[0094] The power source unit 95 receives an interruption (output) from
each of the operation input detection units as a trigger for the return
from the power saving mode to the normal mode. When such an interruption
has taken place, the power source unit 95 restores the supply of power to
the main control unit 9, the image reading unit 1c, the operation panel
1b, the print engine unit 10, the document cover 1a, and the like, and
causes the multifunctional peripheral 100 to return from the power saving
mode to the normal mode (see FIG. 9).

[0095] As illustrated by the dashed line in FIG. 9, in order for the power
source unit 95 to return to the normal mode, the power source unit 95
(the switch unit 98) still supplies power to each of the operation input
detection units during the power saving mode as well.

[0096] The communication unit 94, which is an operation input detection
unit, generates an interruption upon receiving image data or the like
from the external computer 200, and inputs the interruption to the power
source unit 95 (the interruption A in FIG. 10). The touch panel unit 12
also generates an interruption in response to a touch operation by the
user, and inputs the interruption to the power source unit 95 (the
interruption B in FIG.10). The operation panel 1b may also generate an
interruption whenever any of the hard keys is pressed, and may input the
interruption to the power source unit 95. The insertion/removal detection
sensor 16s also generates an interruption, upon detecting removal or
attachment due to paper supply or replacement, and inputs the
interruption to the power source unit 95 (the interruption C in FIG.10).
The cover open/close detection sensor 1fs also generates an interruption,
upon detecting operation (opening/closing) of the cover of a chassis for
maintenance, for replacement of consumed goods, or for handling a paper
jam, and inputs the interruption to the power source unit 95 (the
interruption D in FIG.10). The open/close detection sensor 1cs (the
interruption E in FIG.10), which detects the raising or lowering of the
document cover 1a, also generates an interruption upon detecting an
operation of the document cover 1a (the placing of a document thereon or
raising or lowering thereof) for copying or the like, and inputs the
interruption to the power source unit 95.

[0097] When there is an input (interruption) from each of the operation
input detection units, the power source unit 95 restores the supply of
power to the main control unit 9 and the like, and causes the
multifunctional peripheral 100 to return from the power saving mode to
the normal mode.

[0098] (Flow of the Phase Correction Control for Each of the Polygon
Mirrors 6Bk-6C During the Normal Mode)

[0099] The description shall now relate to the flow of the phase
correction control for each of the polygon mirrors 6Bk-6C during the
normal mode of the multifunctional peripheral 100 of the present
embodiment, with reference to FIGS. 11 to 14. FIG. 11 is a flow chart for
illustrating one example of the flow for the phase correction control of
each of the polygon mirrors 6Bk-6C during the normal mode. FIG. 12 is a
timing chart for illustrating one example of a detection signal outputted
by the light-receiving units 8 before the start of phase correction. FIG.
13 is a timing chart for illustrating one example of the detection signal
outputted by the light-receiving units 8 during the phase correction
control. FIG. 14 is a timing chart for illustrating one example of the
detection signal outputted by the light-receiving units 8 after the
completion of the phase correction.

[0100] In the description below, the description relates to an example in
which black serves as the reference color, and the phases of the polygon
mirrors 6Y, 6M, 6C (the polygon motors 7Y, 7M, 7C) for the other colors
(the colors targeted for phase correction, more specifically, yellow,
magenta, and cyan) are matched to the phase of the polygon mirror 6Bk
(the polygon motor 7Bk) for the reference color. The reference color may,
however, be any one of the four colors.

[0101] The description shall firstly relate to the phase correction
control for each of the polygon mirrors 6Bk-6C during the normal mode.
The "start" in FIG. 11 is a point in time at which a print job is started
in the normal mode in response to the receipt of pressing down of the
start key 14 on the operation panel 1b or of printing data from the
computer 200.

[0102] Upon completion of the print job, each of the polygon motors 7Bk-7C
is stopped. For this reason, the phase correction control of each of the
polygon mirrors 6Bk-6C is carried out at the start time of each print
job. When print jobs are being continuously executed, each of the polygon
motors 7Bk-7C need not be stopped. For this reason, when the print jobs
are being continuously carried out, the phase correction control for each
of the polygon mirrors 6Bk-6C may also be carried out only before the
first of the print jobs is started.

[0103] At the start of a print job, the engine control unit 90 causes each
of the polygon motors 7Bk-7C to rotate (step #1). More specifically, the
engine control unit 90 causes the drive signal generation unit 902 to
supply (input) to each of the polygon motors 7Bk-7C a drive signal of a
predetermined reference period (frequency). Then, the engine control unit
90 checks whether or not the polygon motors 7Bk-7C are in a state of
rotating at the same speed (step #2). More specifically, for example, the
engine control unit 90 checks whether or not the synchronization signal
is being outputted to the drive signal generation unit 902 from all of
the polygon motors 7.

[0104] In the event that each of the polygon motors 7Bk-7C is not rotating
at the same speed ("No" in step #2), the flow returns to step #1. On the
other hand, when each of the polygon motors 7Bk-7C is in a state of
rotating at the same speed ("Yes" in step #2), the engine control unit 90
detects and measures a time difference Δ1 between a detection
signal BD1 detected by the light-receiving unit 8 for the reference color
(for example, black) and a detection signal BD2 detected by a
light-receiving unit 8 for a color which is later to undergo phase
correction, from among those colors that have not yet undergone phase
correction (step #3).

[0105] The description now relates to the detection of the time difference
Δ1 prior to the start of phase correction, with reference to FIGS.
12 to 14. Firstly, in association with the completion of a print job,
each of the polygon motors 7Bk-7C is stopped. The phase of each of the
polygon mirrors 6Bk-6C (each of the polygon motors 7Bk-7C) upon being
stopped is not always constant, and in some cases they are stopped while
in respectively different states. Also, even though each of the polygon
motors 7Bk-7C first begins to rotate at the same time, in some cases the
phase differences when each of the polygon motors 7Bk-7C reaches a state
of rotating at the same speed are also respectively different, due in
part to differences in the properties thereof

[0106] Herein, in the multifunctional peripheral 100 of the present
embodiment, there is only one correction current supply unit 51 provided.
The correction current supply unit 51, during the scanning and exposure
of a single line, changes the magnitude of the currents so as to be the
same, and supplies currents of the same magnitude to each of the
laser-light-emitting units 5Bk-5C. However, when there is a large shift
in the phases of each of the polygon mirrors 6Bk-6C (each of the polygon
motors 7Bk-7C), the scanning positions of the laser beams directed to the
photosensitive drums 22 at the same point in time are far apart. For
example, it is sometimes the case that although a central portion of a
photosensitive drum 22 in the axial direction is being scanned with a
certain color, the end parts of the photosensitive drum 22 in the axial
direction are being scanned with another color. When this occurs, the
laser beam can no longer be appropriately corrected in accordance with
the scanning position of the photosensitive drum 22 (the scanning
position in the main scanning direction). It is also sometimes the case
that there is a variation in the write position for the first pixel of a
line when there is a large variation in the phases of each of the polygon
mirrors 6Bk-6C (each of the polygon motors 7Bk-7C).

[0107] Thus, in the present embodiment, each of the polygon mirrors 6Bk-6C
(each of the polygon motors 7Bk-7C) undergoes phase correction to bring
the phase differences for each of the polygon mirrors 6Bk-6C within an
acceptable range. In the multifunctional peripheral 100 of the present
embodiment, the phase correction is carried out on the basis of the
detection signal of the laser beams by each of the light-receiving units
8Bk-8C.

[0108] Firstly, as illustrated in FIGS. 12 to 14, in the multifunctional
peripheral 100 of the present embodiment, each of the light-receiving
units 8Bk-8C produces an output "High" in a state where a laser beam is
not being irradiated. In a state where a laser beam is being irradiated,
each of the light-receiving units 8Bk-8C produces an output "Low." In
other words, the output of each of the light-receiving units 8Bk-8C falls
when irradiation with a laser beam is detected. The positive and negative
of this logic may also be reversed.

[0109] The detection signal BD1 in FIGS. 12 to 14 illustrates one example
of the waveform of a signal outputted by a light-receiving unit 8 of the
reference color (for example, black). Meanwhile, the detection signal BD2
illustrates one example of the waveform of a signal outputted by a
light-receiving unit 8 of a color targeted for phase correction (yellow,
cyan, or magenta).

[0110] As illustrated in FIG. 12, at the start of the phase correction,
the engine control unit 90 detects (measures) the time difference
Δ1 between the change points (falling edges) of the detection
signal BD1 of the reference color and the detection signal BD2 of the
color targeted for phase correction (step #3). For example, the time
difference Δ1 is measured by an engine CPU 903 or timing unit 904
provided to the engine control unit 90. In the present embodiment, the
absolute value of this time difference Δ1 is brought into the
acceptable range (for example, several μ is, or about 1-3 μs) to
thereby bring the phase difference into an acceptable range.

[0111] Next, the engine control unit 90 checks whether or not the absolute
value of the measured time difference Δ1 is greater than a
predetermined threshold TH1 (for example, about 10-20 μs) (step #4).
The threshold TH1 is a threshold for determining whether to perform a
rough adjustment process or to perform a fine adjustment process
(described below), and the value can be determined as desired. A closer
proximity of the threshold TH1, which is greater than the predetermined
acceptable range, to the predetermined acceptable range correlates to a
shorter time needed for the phase correction.

[0112] In the event that the absolute value is greater than the
predetermined threshold TH1 ("Yes" in step #4), the engine control unit
90 uses the rough adjustment process to shrink the phase difference
between the polygon mirror 6 for the reference color (the polygon motor
7Bk) and the polygon mirrors 6Y, 6M, 6C (polygon motors 7Y, 7M, 7C) for
the colors targeted for phase correction (step #5). By contrast, when the
absolute value is not greater than the predetermined threshold TH1 ("No"
in step #4), the engine control unit 90 uses the fine adjustment process
to shrink the phase difference (time difference Δ1) between the
polygon mirror 6Bk for the reference color and the polygon mirrors 6Y,
6M, 6C for the colors targeted for phase correction (step #6).

[0113] The description now relates to the rough adjustment process and the
fine adjustment process. Firstly, in both the rough adjustment process
and the fine adjustment process, the engine control unit 90 adjusts the
phase (frequency) of the drive signal supplied to the polygon motors 7Y,
7M, 7C for the colors targeted for phase correction, and shrinks the time
difference Δ1 between the detection signal BD1 and the detection
signal BD2 (the phase difference of the polygon mirrors 6).

[0114] More specifically, when the phase of the detection signal BD2 is
delayed relative to the detection signal BD1 for the reference color, the
engine control unit 90 causes the drive signal generation unit 902 to
make the period of the drive signal for the colors targeted for phase
correction shorter than the reference period. The engine control unit 90
then causes a drive signal of a shorter period than the reference period
to be supplied to the polygon motors 7Y, 7M, 7C for the colors targeted
for phase correction, and advances the phase of the detection signal BD2.

[0115] By contrast, when the phase of the detection signal BD2 is advanced
relative to the detection signal BD1 for the reference color, the engine
control unit 90 causes the drive signal generation unit 902 to make the
period of the drive signal for the colors targeted for phase correction
shorter than the reference period. The engine control unit 90 then causes
a drive signal of a longer period than the reference period to be
supplied to the polygon motors 7Y, 7M, 7C for the colors targeted for
phase correction, and delays the phase of the detection signal BD2.

[0116] Herein, the change amount relative to the reference period is
different for the rough adjustment process and the fine adjustment
process. The period change amount in the rough adjustment process (a
first period change amount) represents a greater period change amount
from the reference period than during the fine adjustment process. By
contrast, the period change amount in the fine adjustment process (a
second period change amount) represents a smaller period change amount
from the reference period than during the rough adjustment process.

[0117] The first period change amount and the second period change amount
are within a range where a loss of control of the rotational speed of the
polygon motors 7 will not occur, and are change amounts that are
arbitrarily determined as desired. For example, when the period change
amount where a loss of control of the rotational speed of the polygon
motors 7 will not occur (desynchronization will not occur) is up to about
0.5% of the period of the drive signal (the reference period), then the
first period change amount would be about 0.5% of the period of the drive
signal for the polygon motors 7 (the reference period), and the second
period change amount would be about 0.2-0.4% (more specifically, about
0.2%) of the period of the drive signal for the polygon motors 7 (the
reference period).

[0118] In the rough adjustment process, the engine control unit 90 causes
the drive signal generation unit 902 to generate a drive signal with
which the period of the drive signal for the colors targeted for phase
correction has been shorted or lengthened by as much as the first period
change amount, depending on whether the phase is to be advanced or
delayed. By contrast, in the fine adjustment process, the engine control
unit 90 causes the drive signal generation unit 902 to generate a drive
signal with which the period of the drive signal for the colors targeted
for phase correction has been shorted or lengthened by as much as the
second period change amount, depending on whether the phase is to be
advanced or delayed. Thus, the rough adjustment process is able to
eliminate the time difference Δ1 between the detection signal BD1
and the detection signal BD2 (is able to bring the phases of the
different polygon mirrors 6 closer together) more rapidly than the fine
adjustment process.

[0119] Therefore, when the rough adjustment process is to be carried out
(step #5), the engine control unit 90 checks whether or not the absolute
value of the time difference Δ1 between the detection signal BD1
and the detection signal BD2 has reached the predetermined threshold TH1
or lower every instance when the detection signal BD1 and the detection
signal BD2 are inputted (step #7).

[0120] In the event that the absolute value is greater than the threshold
TH1 ("No" in step #7), the engine control unit 90 continues to use the
rough adjustment process to eliminate the time difference Δ1 (the
flow returns to step #5). On the other hand, when the absolute value has
reached the threshold TH1 or lower ("Yes" in step #7), the engine control
unit 90 carries out the fine adjustment process (step #6).

[0121] When a transition is made to a stage where the fine adjustment
process is to be carried out (step #6), the engine control unit 90 checks
whether or not the absolute value of the time difference Δ1 between
the detection signal BD1 and the detection signal BD2 has reached the
predetermined acceptable range or lower (has fallen into the acceptable
range) every instance when the detection signal BD1 and the detection
signal BD2 are inputted (step #8).

[0122] As illustrated in FIG. 13, the fine adjustment process is performed
when the absolute value of the time difference Δ1 between the
detection signal BD1 and the detection signal BD2 reaches the threshold
TH1 or lower. The fine adjustment process, as illustrated in FIG. 14,
causes the absolute value of the time difference Δ1 between the
detection signal BD1 and the detection signal BD2 to fall within the
acceptable range.

[0123] In the event that the time difference Δ1 has not reached the
acceptable range or lower ("No" in step #8), the engine control unit 90
continues to use the fine adjustment process to eliminate the time
difference Δ1 (the flow returns to step #6). By contrast, when the
time difference Δ1 has reached the acceptable range or lower ("Yes"
in step #8), the engine control unit 90 has completed the phase
correction for the one color (step #9). The engine control unit 90 makes
the drive signal generation unit 902 cause the period of the drive signal
for the polygon motor 7 of the color targeted for phase correction for
which phase correction has been completed to return to the reference
period. Thus, the polygon mirror 6Bk (polygon motor 7Bk) of the reference
color and the polygon mirror 6 (polygon motor 7) of the color for which
the phase has been corrected continue to rotate at substantially the same
phase and the same rotational speed.

[0124] In this manner, because the fine adjustment process ultimately
brings the time difference Δ1 within the acceptable range, the
phase correction is performed with a period change amount (increment
size) that is shorter (smaller) than in the rough adjustment process. As
such, the phase difference between the polygon mirror 6Bk of the
reference color and the polygon mirrors 6Y, 6M, 6C of the colors targeted
for phase correction can be accurately corrected.

[0125] After step #9, the engine control unit 90 checks whether correction
has been completed for all of the polygon mirrors 6Y, 6M, 6C of the
colors targeted for phase correction (step #10). In the event that
correction has been completed ("Yes" in step #10), the flow is
terminated, and in the event that correction has not been completed ("No"
in step #10), the flow returns step #3. The correction of the phase
difference for the colors targeted for phase correction may also be
carried out for a plurality of colors in parallel (at the same time).

[0126] (Flow of the Phase Correction Control when the Main Power Source is
Turned on or at the Time of Return to the Normal Mode)

[0127] The description shall now relate to the flow of the phase
correction control for each of the polygon mirrors 6Bk-6C when the main
power source is turned on or at the time of return to the normal mode in
the multifunctional peripheral 100 of the present embodiment, with
reference to FIGS. 15 and 16. FIGS. 15 and 16 are flow charts
illustrating one example of a flow for the phase correction control of
each of the polygon mirrors 6Bk-6C when the main power source is turned
on or at the time of return to the normal mode.

[0128] When the main power source is turned on or at the time of return to
the normal mode, a variety of processes are performed to bring the
multifunctional peripheral 100 to a state where printing is possible,
such as start-up of the main control unit 9, start-up of the engine, and
increasing the temperature of the fixing unit 3b.

[0129] However, for example, when the main power source is turned on, the
phase correction of each of the polygon mirrors 6Bk-6C is in some cases
performed as an initial operation. It is necessary for the phase
correction for each of the polygon mirrors 6Bk-6C to be performed in a
case where the return to the normal mode is based on a print job, such as
a case where the return from the power saving mode to the normal mode is
in response to the receipt of the printing data from the computer 200, or
a case where a print command has been made to the operation panel 1b in
association with the return from the power saving mode to the normal
mode.

[0130] When the main power source is turned on or at the time of the
return to the normal mode, the warming of the fixing unit 3b (warm-up of
the fixing unit 3b) is one process that requires time in order to reach a
state where printing is possible. In general, a temperature detector is
provided in order to detect the temperature of the fixing unit 3b (for
example, the temperature of the heating roller 37). In the
multifunctional peripheral 100 of the present embodiment, too, a
temperature sensor 39 is provided (see FIG. 1). For example, the
temperature sensor 39 includes a thermistor, and the voltage outputted is
different depending on the temperature. The output of the temperature
sensor 39 is then inputted to the engine control unit 90 (see FIG. 4).

[0131] The engine control unit 90 recognizes the temperature of the fixing
unit 3b on the basis of the output of the temperature sensor 39. In the
normal mode, the engine control unit 90 turns on/off the distribution of
power to a heater built into the heating roller 37, to maintain the
temperature of the fixing unit 3b at a temperature where fixing is
possible (a fixing control temperature, for example, about
170-200° C., varies depending on the type of machine).

[0132] In the "off" state of the main power source or during the power
saving mode, no power is supplied to the heater for warming up the
heating roller 37 of the fixing unit 3b. As such, the result is that the
fixing unit 3b cools down entirely to room temperature. A duration of
about several seconds to several tens of seconds is in some cases needed
in order to warm (the heating roller 37 of) the fixing unit 3b from the
entirely cooled-down state to the fixing control temperature. The time
needed to warm up to the fixing control temperature may differ depending
on the heater output, the heating control temperature, or the material
properties of the member of the fixing unit 3b.

[0133] As such, because time is needed in order to warm up the fixing unit
3b, in some cases the phase correction of each of the polygon mirrors
6Bk-6C (each of the polygon motors 7Bk-7C) need not be the briefest
possible (need not be rushed) when the main power source is turned on or
at the time of return to the normal mode.

[0134] Thus, in the multifunctional peripheral 100 of the present
embodiment, when the phase correction of each of the polygon mirrors
6Bk-6C (each of the polygon motors 7Bk-7C) need not be the briefest
possible when the main power source is turned on or at the time of return
to the normal mode, then a base period of the drive signal is changed by
a period change amount even lesser than that of the fine adjustment
process (by a third period change amount) to perform phase correction.

[0135] The description shall now, with reference to FIG. 15, first relate
to the flow of the phase correction control for each of the polygon
mirrors 6Bk-6C when the temperature of the fixing unit 3b has dropped,
such as at the warm-up start time for the fixing unit 3b, when the main
power source is turned on or at the time of return to the normal mode.

[0136] Firstly, at a time such as the warm-up start time for the fixing
unit 3b when the main power source is turned on or at the time of return
to the normal mode, the engine control unit 90 ascertains whether or not
the temperature of the fixing unit 3b has dropped by whether or not the
temperature of the fixing unit 3b falls short of a predetermined first
temperature, on the basis of the output of the temperature sensor 39. The
first temperature can be determined arbitrarily as desired, but one
example would be several tens of degrees Celsius or lower, more
specifically, 40° C. or lower. In other words, the first
temperature is a temperature at which the fixing unit 3b has cooled to an
extent that the phase correction can be completed before the warm-up of
the fixing unit 3b is completed even when the phase correction is carried
out only with an ultrafine adjustment process.

[0137] When the phase correction control for each of the polygon mirrors
6Bk-6C is carried out when the main power source is turned on or at the
time of return to the normal mode, the engine control unit 90 recognizes
whether the temperature of the fixing unit 3b has fallen short of the
first temperature on the basis of the output of the temperature sensor
39.

[0138] The "start" in FIG. 15 is a point in time, such as when the main
power source is turned on, the time of return to the normal mode, or the
warm-up start time for the fixing unit 3b, where the temperature of the
fixing unit 3b has fallen short of the first temperature and where the
phase correction of each of the polygon mirrors 6Bk-6C (each of the
polygon motors 7Bk-7C) begins when the temperature of the fixing unit 3b
has dropped, on the basis of the output of the temperature sensor 39.

[0139] Firstly, the engine control unit 90 causes each of the polygon
motors 7Bk-7C to rotate (step #11). Then, the engine control unit 90
checks whether each of the polygon motors 7Bk-7C is in a state of
rotating at the same speed (step #12). Step #11 and step #12 are similar
to during the normal mode, and a more detailed description thereof has
been omitted (see FIG. 11).

[0140] When each of the polygon motors 7Bk-7C is not yet rotating at the
same speed ("No" in step #12), the flow returns to step #11. On the other
hand, when each of the polygon motors 7Bk-7C is in a state of rotating at
the same speed ("Yes" in step #12), the engine control unit 90 uses the
ultrafine adjustment process to shrink the phase difference between the
polygon mirror 6Bk (polygon motor 7Bk) of the reference color and the
polygon mirror 6Y, 6M, 6C (polygon motor 7Y, 7M, 7C) of one color from
among those colors that have not yet undergone phase correction (step
#13).

[0141] The description now relates to the ultrafine adjustment process. In
the ultrafine adjustment process, the period change amount from the
reference period is made to be the third period change amount, which is
even lesser than that during the fine adjustment process (than the second
period change amount). The third period change amount, too, is within a
range where a loss of control of the rotational speed of the polygon
motors 7 will not occur, and is a change amount that is arbitrarily
determined as desired. One example of the third period change amount
would be about 0.1% of the reference period.

[0142] In the ultrafine adjustment process, the engine control unit 90
causes the drive signal generation unit 902 to generate a drive signal
with which the period of the drive signal for the colors targeted for
phase correction has been shorted or lengthened by as much as the third
period change amount, depending on whether the phase is to be advanced or
delayed. This makes it possible to bring the time difference Δ1
between the detection signal BD1 and the detection signal BD2 within the
acceptable range in an even finer manner than the fine adjustment process
(makes it possible to bring the phases of each of the polygon mirrors
6Bk-6C closer to each other in an even finer manner).

[0143] The engine control unit 90 then checks whether or not (the absolute
value) of the time difference Δ1 between the detection signal BD1
and the detection signal BD2 has reached the predetermined acceptable
range or lower (has fallen into the acceptable range) every instance when
the detection signal BD1 and the detection signal BD2 are inputted (step
#14).

[0144] In the event that the time difference Δ1 has not fallen into
the acceptable range ("No" in step #14), the engine control unit 90
continues to use the ultrafine adjustment process to eliminate the time
difference Δ1 (the flow returns to step #13). However, when time
difference Δ1 has reached the acceptable range or lower ("Yes" in
step #14), the engine control unit 90 has completed the phase correction
for one color (step #15). At such a time, the engine control unit 90
makes the drive signal generation unit 902 cause the period of the drive
signal for the polygon motor 7 of the color targeted for phase correction
for which phase correction has been completed to return to the reference
period. Thus, the polygon mirror 6Bk (polygon motor 7Bk) of the reference
color and the polygon mirrors 6Y, 6M, 6C (polygon motors 7Y, 7M, 7C) of
the colors targeted for phase correction continue to rotate at
substantially the same phase and the same rotational speed.

[0145] In this manner, because the ultrafine adjustment process ultimately
brings the time difference Δ1 within the acceptable range, the
phase correction is performed with an increment size that is shorter
(smaller) than in the fine adjustment process. As such, the phase
difference between the polygon mirror 6Bk (polygon motor 7Bk) of the
reference color and the polygon mirrors 6Y, 6M, 6C (polygon motors 7Y,
7M, 7C) of the colors targeted for phase correction can be accurately
corrected.

[0146] After step #15, the engine control unit 90 checks whether
correction has been completed for all of the polygon mirrors 6Y, 6M, 6C
of the colors targeted for phase correction (step #16). In the event that
correction has been completed ("Yes" in step #16), the flow is
terminated, and when correction has not been completed ("No" in step
#16), the flow returns step #13.

[0147] The description shall now, with reference to FIG. 16, relate to the
flow of the phase correction control for each of the polygon mirrors
6Bk-6C when the temperature of the fixing unit 3b has decreased by a
certain degree at such a time as when the main power source is turned on,
at the time of return to the normal mode, or at the warm-up start time
for the fixing unit 3b.

[0148] Firstly, at a time such as the warm-up start time for the fixing
unit 3b when the main power source is turned on or at the time of return
to the normal mode, the engine control unit 90 ascertains whether or not
the temperature of the fixing unit 3b has decreased by a certain degree,
by whether or not the temperature of the fixing unit 3b is not less than
the predetermined first temperature and not greater than a second
temperature, on the basis of the output of the temperature sensor 39. The
second temperature can be determined arbitrarily as desired, but one
example would be one hundred and several tens of degrees Celsius. In
other words, the question of whether or not the phase correction can be
completed before the warm-up of the fixing unit 3b is completed when the
ultrafine adjustment process is to be performed is ascertained using the
first temperature and the second temperature.

[0149] When the fixing unit 3b surpasses the second temperature, the same
process as the phase correction control for each of the polygon mirrors
6Bk-6C during the normal mode illustrated in FIG. 11 (a phase correction
combining both the rough adjustment process and the fine adjustment
process) is performed (see FIG. 11).

[0150] The "start" in FIG. 16 is a point in time, such as the warm-up
start time for the fixing unit 3b when the main power source is turned on
or the time of return to the normal mode, where the engine control unit
90 starts the phase correction for the polygon mirrors 6Y, 6M, 6C for the
colors targeted for phase correction, upon ascertaining that the
temperature of the fixing unit 3b is not less than the predetermined
first temperature and not greater than the second temperature (that the
temperature of the fixing unit 3b has dropped by a certain degree), on
the basis of the output of the temperature sensor 39.

[0151] Firstly, the engine control unit 90 causes each of the polygon
motors 7Bk-7C to rotate (step #21). Then, the engine control unit 90
checks whether or not the polygon motors 7Bk-7C are in a state of
rotating at the same speed (step #22). Step #21 and step #22 are similar
to during the normal mode, and a more detailed description thereof has
been omitted (see FIG. 11).

[0152] In the event that each of the polygon motors 7Bk-7C is not yet
rotating at the same speed ("No" in step #22), the flow returns to step
#21. On the other hand, when each of the polygon motors 7Bk-7C is in a
state of rotating at the same speed ("Yes" in step #22), the engine
control unit 90 detects the time difference Δ1 between the
detection signal BD1 detected by the light-receiving unit 8 for the
reference color and the detection signal BD2 detected by the
light-receiving unit 8 for a color which is later to undergo phase
correction, from among those colors that have not yet undergone phase
correction (step #23). More specifically, at the start of the phase
correction, the engine control unit 90 detects (measures) the time
difference A 1 between the change points (falling edges) of the detection
signal BD1 of the reference color and the detection signal BD2 of the
color targeted for phase correction (step #23).

[0153] The approach to the phase correction is similar to the phase
correction during the normal mode as described with reference to FIGS. 12
to 14, and thus a description thereof has been omitted.

[0154] Next, the engine control unit 90 checks whether or not the absolute
value of the measured time difference Δ1 is greater than the
predetermined threshold TH1 (for example, about 10-20 μs) (step #24).
In the effect that the absolute value is greater than the predetermined
threshold TH1 ("Yes" in step #24), the engine control unit 90 uses the
rough adjustment process to shrink the phase difference between the
polygon mirror 6Bk (polygon motor 7Bk) of the reference color and the
polygon mirror 6Y, 6M, 6C (polygon motor 7Y, 7M, 7C) of any of the colors
targeted for phase correction (step #25). On the other hand, when the
absolute value is not greater than the predetermined threshold TH1 ("No"
in step #24), the engine control unit 90 uses the ultrafine adjustment
process to shrink the phase difference between the polygon mirrors 6
(polygon motors 7) of the reference color and of the color targeted for
phase correction (step #26).

[0155] In other words, when the main power source is turned on or at the
time of return to the normal mode, when the engine control unit 90
ascertains that the temperature of the fixing unit 3b has dropped by a
certain degree on the basis of the output of the temperature sensor 39
and of the predetermined first temperature and second temperature, then
the fine control process during the normal mode is changed and the
ultrafine adjustment process using the third period change amount is
carried out.

[0156] When the rough adjustment process is being carried out (step #25),
the engine control unit 90 checks whether or not the absolute value of
the time difference Δ1 between the detection signal BD1 and the
detection signal BD2 has reached the predetermined threshold TH1 or
lower, at every instance when the detection signal BD1 and the detection
signal BD2 are inputted (step #27). Step #27 to step #30 are similar to
step #7 to step #10 during the phase correction in the normal mode as
described with reference to FIG. 11, and it is possible to call upon the
description thereof. A more detailed description has thus been omitted.

[0157] The image-forming apparatus of the present embodiment (for example,
the multifunctional peripheral 100) thus includes a plurality of
photosensitive drums 22 provided for every color (22Bk-22C), a plurality
of laser scanning units 40 (laser scanning units 40bk-40C) for scanning
and exposing the corresponding photosensitive drum 22 (22Bk-22C) and
forming a toner image of respectively different colors, each of the laser
scanning units 40 including a laser-light-emitting unit 5 for switching a
laser beam on and off in accordance with image data, a polygon mirror 6
for reflecting, while rotating, the laser beam emitted by the
laser-light-emitting unit 5 and scanning and exposing the corresponding
photosensitive drum 22 (22Bk-2CC), the polygon mirror having a plurality
of reflective surfaces, a polygon motor 7 for rotating the polygon mirror
6, the rotational speed of the polygon motor changing in accordance with
the frequency of a provided drive signal, and a light-receiving unit 8
for outputting a detection signal having an output value which changes
when the laser beam is received, the light-receiving unit being provided
within a range in which the laser beam is irradiated by the polygon
mirror 6, and a motor control unit (engine control unit 90) for providing
the drive signal of a predetermined base period to the polygon motors 7
and causing the polygon motors 7 to rotate such that each of the polygon
motors 7 (polygon motors 7Bk-7C) rotates at the same speed, detecting the
time difference Δ1 between a change point of the detection signal
BD1 of the laser scanning unit of a reference color (the laser scanning
unit 40Bk) and the change points of the detection signals BD2 of the
laser scanning units of colors targeted for phase correction other than
the reference color (laser scanning units 40Y, 40M, 40C), and, when the
absolute value of the time difference Δ1 is greater than a
predetermined threshold TH1, carrying out a rough adjustment process in
which the drive signal with which the base period has been shorted or
lengthened by a first period change amount causes the polygon motors of
the colors targeted for phase correction (polygon motors 7Y, 7M, 7C) to
rotate and causes the time difference Δ1 to decrease, or, when the
absolute value is not greater than the threshold TH1, carrying out a fine
adjustment process in which, until the time difference Δ1 falls
within a predetermined acceptable range, the drive signal with which the
base period has been shortened or lengthened by a second period change
amount smaller than the first period change amount with respect to the
base period causes the polygon motors of the colors targeted for phase
correction (the polygon motors 7Y, 7M, 7C) to rotate and causes the time
difference Δ1 to decrease.

[0158] Thus, the phase differences (time difference Δ1) between the
polygon mirrors 6 of the reference color and of the colors targeted for
phase correction are swiftly and rapidly brought closer to each other by
the rough adjustment process, and thereafter the phase differences (time
difference Δ1) between the polygon mirrors 6 of the reference color
and of the colors targeted for phase correction are accurately and
precisely corrected (adjusted) by the fine adjustment process. As such,
the time needed to correct the phase differences can successfully be
curtailed as much as possible, and yet the phase differences can still be
corrected accurately.

[0159] The image-forming apparatus (for example, the multifunctional
peripheral 100) also includes one correction current supply unit 51 for
changing, in a similar manner for each of the laser-light-emitting units
5, the current flowing to each of the laser-light-emitting units 5
(laser-light-emitting units 5Bk-5C) in accordance with the scanning
position in the main scanning direction, and for changing the light
emission level of each of the laser-light-emitting units 5 to correct the
difference in energy received by the photosensitive drums 22 (22Bk-22C)
in the main scanning direction. In the present disclosure, the phase
difference of each of the polygon mirrors 6Bk-6C (each of the polygon
motors 7Bk-7C) is adjusted, and all of the plurality of polygon mirrors 6
are made to rotate in synchronization. The scanning and exposure
positions of the photosensitive drums 22 are thereby made to be
substantially the same position for each color, and accordingly there
need be installed only one correction current supply unit 51 for
performing the same for the laser-light-emitting units 5 of each color,
without the need to provide for every laser-light-emitting unit 5 a
current supply unit for performing a correction in which the amount of
current flowing to each of the laser-light-emitting units 5Bk-5C is
changed dependent on the scanning position. As such, merely providing the
single correction current supply unit 51 makes it possible to suitably
correct the light emission levels of the laser-light-emitting units 5 and
possible to keep low the production costs of the image-forming apparatus.

[0160] Among the processes for achieving a state where the image-forming
apparatus can be used, the process for warming the fixing unit 3b to a
temperature where toner can be fixed (the warm-up process for the fixing
unit 3b) in some cases requires a longer time than does the phase
difference correction. In other words, sometimes there is no need to
attempt to shorten as much as possible the correction of the phase
differences. Therefore, the image-forming apparatus of the present
embodiment (for example, the multifunctional peripheral 100) includes a
transfer unit (the intermediate transfer unit 3a) for transferring while
also superimposing a toner image of each color formed on each of the
photosensitive drums 22 (22Bk-22C) onto paper, and a fixing unit 3b for
fixing the transferred toner image onto the paper with heat, the fixing
unit having a built-in heater, when the warm-up for warming the
temperature of the fixing unit 3b to the temperature needed in order to
fix a toner image is performed, the motor control unit (engine control
unit 90) detects the time difference Δ1 between the change point of
the detection signal BD1 of the laser scanning unit of the reference
color (the laser scanning unit 40Bk) and the change points of the
detection signals BD2 of the laser scanning units of the colors targeted
for phase correction (the laser scanning units 40Y, 40M, 40C), carries
out the rough adjustment process when the absolute value of the time
difference Δ1 is greater than the threshold TH1, and, after the
absolute value has reached the threshold TH1 or lower due to the rough
adjustment process, instead of the fine adjustment process, carries out
an ultrafine adjustment process in which the drive signal with which the
base period has been shortened or lengthened by a third predetermined
period change amount is used to cause the polygon motors (the polygon
motors 7Y, 7M, 7C) of the colors targeted for phase correction to rotate
until the time difference Δ1 falls within the acceptable range. The
third period change amount is a lesser change amount with respect to the
base period than is the second period change amount. Thus, in a case
where time may be allotted to correct the phase correction, the
correction of the phase difference is performed such that the base period
is changed by the third period change amount, which has the least change
amount, and the time difference Δ1 falls within the acceptable
range. As such, because the phase difference is corrected with a lesser
period change amount while consideration is also given to the ability of
the polygon motors 7 to track and respond, the phase difference can be
corrected accurately.

[0161] The image-forming apparatus of the present embodiment (for example,
the multifunctional peripheral 100) also includes a temperature sensor 39
for detecting the temperature of the fixing unit 3b. When the temperature
detected by the temperature sensor 39 at the start of phase correction is
less than a predetermined first temperature, the motor control unit
(engine control unit 90) does not perform the rough adjustment process
but rather the ultrafine adjustment process until the time difference
Δ1 falls within the acceptable range. The phase difference is
thereby corrected with only the ultrafine adjustment process using the
third period change amount in a case where time is needed to warm the
fixing unit 3b and time may be allotted to phase correction, such as a
case where the fixing unit 3b has cooled down entirely. As such,
extremely accurate phase correction can be performed.

[0162] When the temperature detected by the temperature sensor 39 at the
start of phase correction is higher than the predetermined second
temperature, the motor control unit (engine control unit 90) does not
perform the ultrafine adjustment process but rather causes the time
difference Δ1 to fall within the acceptable range using the rough
adjustment process and the fine adjustment process. The second
temperature is a higher temperature than the first temperature. Thus,
when heat has already been accumulated in the fixing unit 3b and the
warming of the fixing unit 3b might be completed in a brief period of
time, the phase correction is performed using the rough adjustment
process and the fine adjustment process, and phase correction is more
rapidly ended.

[0163] The first period change amount, the second period change amount,
and the third period change amount are change amounts for the drive
signal within a range where the rotation of the polygon motors 7 will not
be desynchronized. The period change of the drive signal is thereby
performed in a range where the polygon motors 7 can be controlled.

[0164] The first period change amount is the greatest change amount for
the drive signal within a range where the rotation of the polygon motors
7 will not be desynchronized. When the period change amount where a loss
of control of the rotational speed of the polygon motors 7 will not occur
(desynchronization will not occur) is a range of ±0.5% of the
reference period of the drive signal, then the first period change amount
would be ±0.5% of the period of the drive signal for the polygon
motors 7 (the reference period). This makes it possible for the phase
difference to be brought within the threshold as quickly as possible.

[0165] Preferably, the absolute value of the second period change amount
is not greater than one-half of the absolute value of the first period
change amount and the absolute value of the third period change amount is
not greater than one-half of the absolute value of the second period
change amount. When the first period change amount is ±0.5% (absolute
value 0.5%) of the reference period of the drive signal, then the second
period change amount is ±0.2% (absolute value 0.2%) of the reference
period of the drive signal. When the second period change amount is
±0.2% of the reference period of the drive signal, then the third
period change amount is ±0.1% (absolute value 0.1%) of the reference
period of the drive signal. Thus, the rotational speeds of the polygon
motors can be adequately changed in accordance with each of the period
change amounts, and the phase difference can be accurately and quickly
corrected.

[0166] The foregoing is a description of an embodiment of the present
disclosure, but the scope of the present disclosure is not limited
thereto, but rather a variety of modifications can be additionally
carried out within a scope that does not depart from the spirit of the
disclosure.